We are attempting to reach an understanding of the transduction of visible electromagnetic radiation into electrochemical signals generated by the rods and cones of the human eye and the amplification and modification of these signals as they are transmitted through the retina. To achieve our objectives we are studying the following characteristics of human vision: the electrochemical events immediately following the cessation of photic stimulation (after-images and dark adaptation); the pooling and integration of nerve signals at the interfaces of receptor mechanisms (rod-cone interactions, red-green interactions and temporal wavelength modulation sensitivity); the quantum efficiency of isolated receptor systems (normal and anomalous cone photopigment densities and sensitivities); and the genetic variability of receptor system spectral sensitivities (pseudonormal color vision phenotypes, the red-green ratio and normal color vision polymorphism).